1. Field of the Invention
The present invention relates to a wiring board composed of a flexible and insulating substrate and conductor wirings provided thereon, such as a tape wiring board, and a method for producing the wiring board.
2. Description of the Related Art
As a type of package module that employs a tape wiring board, for example, a COF (Chip On Film) is known. In the COF, a semiconductor chip is mounted on a flexible and insulating tape wiring board, and the mounted portion is protected by sealing with a resin. The tape wiring board includes, as major elements, an insulating film substrate, and a number of conductor wirings formed on a surface thereof. In general, the film substrate is made of polyimide, and the conductor wiring is made of copper.
A major application of the COF is an implementation as a display panel driver for a liquid crystal panel or the like. In this case, conductor wirings on a tape wiring board are arranged and divided into a first group that forms external terminals for output signals, and a second group that forms external terminals for input signals, and a semiconductor chip is mounted between the two groups of conductor wirings. An example of such a tape wiring board is illustrated in FIG. 10.
FIG. 10 is a plan view of a tape wiring board including a plurality of semiconductor chip mount portions. 1 indicates a flexible and insulating substrate, and 2 and 3 indicate first and second feeding electrodes provided along both sides in a longitudinal direction of the substrate. A plurality of feeding bus lines 4 are formed, extending in a traverse direction of the insulating substrate 1, and are connected to the first and second feeding electrodes 2 and 3. Pairs of adjacent feeding bus lines 4 section the insulating substrate 1 into a plurality of unit regions, and a semiconductor chip mount portion 5 is provided in each unit region.
A plurality of conductor wirings 6, 7 and 8 are formed on the insulating substrate 1 for each unit region. Inner leads 6a, 7a and 8a formed by one-side end portions of the conductor wirings 6, 7 and 8 are arranged and aligned in the semiconductor chip mount portion 5, and the other-side end portions of the conductor wirings 6, 7 and 8 are connected to the feeding bus lines 4. The inner leads 6a, 7a and 8a are provided with protruding electrodes 9, 10 and 11, respectively. The protruding electrodes 9, 10 and 11 are arranged so as to match electrode pads of the semiconductor chip.
The inner leads 6a of the conductor wirings 6 form the first group, and the inner leads 7a and 8a of the conductor wirings 7 and 8 form the second group. The inner leads 6a of the first group and the inner leads 7a and 8a of the second group are arranged and aligned in the traverse direction of the insulating substrate 1 so that the tips of the inner leads 6a and the tips of the inner leads 7a and 8a face each other. For example, the first group is connected to the electrode pads on the output side of the semiconductor chip, and the second group is connected to the electrode pads on the input side of the semiconductor chip.
According to the tape wiring board, the electrode pads of the semiconductor chip that are divided into two groups of an input-side and an output-side facing each other, can be connected via the protruding electrodes 9, 10 and 11 to the inner lead 6a, 7a and 8a with high connection reliability. Note that, after mounting a semiconductor chip, the conductor wirings 6, 7 and 8 and the feeding bus line 4 are cut and separated from each other for use.
A method for producing a tape carrier board having the above-described configuration hereinafter will be described. Initially, an insulating substrate on a surface of which a plurality of conductor wirings are formed and aligned, is prepared. A photoresist layer is formed on an entire surface of the insulating substrate, and an elongate hole-shaped pattern (an opening) that extends across the conductor wirings is formed in the photoresist layer. Thereby, a portion of the conductor wirings is exposed in the elongate hole-shaped pattern. Next, the exposed portion of the conductor wirings in the elongate hole-shaped pattern of the photoresist is subjected to metal plating to form protruding electrodes. After removing the photoresist, a tape wiring board in which the protruding electrode is formed on the conductor wirings is obtained (see JP 2003-243455 A).
FIG. 11 illustrates the protruding electrodes formed by plating. FIG. 11 corresponds to a portion of the tape wiring board of FIG. 10, and the protruding electrodes 9, 10 and 11 are formed on the inner leads 6a, 7a and 8a, respectively.
The plating is performed using a plating apparatus as illustrated in FIG. 12. FIG. 12 is a cross-sectional view illustrating the plating apparatus schematically. The insulating substrate 1 is conveyed in a plating bath 20 by transport rollers 21a to 21f. The plating bath 20 is filled with a plating solution 22, and an anode 23 is provided in the plating bath 20. A current feeding roller 24 is provided near an inlet of the plating bath 20. The current feeding roller 24 contacts the first and second feeding electrodes 2 and 3 on the insulating substrate 1 (see FIG. 10), thereby feeding electric power. On the other hand, the current feeding roller 24 is connected to a plating power supply 26. The plating power supply 26 is connected via a first plating wiring conductor 25 to the anode 23. The plating power supply 26 supplies a first plating current I0.
The current feeding roller 24 has a structure as illustrated in FIG. 13. The current feeding roller 24 comprises an insulating roller 27, and first and second ring-shaped electrodes 28 and 29 that are provided circumferentially at both end portions of the insulating roller 27 and are insulated from each other. The first ring-shaped electrode 28 of the current feeding roller 24 is caused to face and contact the first feeding electrode 2 on the insulating substrate 1, and the second ring-shaped electrode 29 is caused to face and contact the second feeding electrode 3 on the insulating substrate 1, thereby feeding electric power. The first ring-shaped electrode 28 and the second ring-shaped electrode 29 are connected together to the first plating wiring conductor 25.
The pitches of the electrode pads on a semiconductor chip are not necessarily uniform. Therefore, the intervals of the protruding electrodes on the tape carrier board have to be broadened or narrowed as illustrated in FIG. 10. The inner leads 6a of the first group in FIG. 10 have a uniform and dense wiring pitch. The inner leads of the second group include the inner leads 7a having the same dense wiring pitch as that of the inner leads 6a of the first group (dense pitch region), and the inner leads 8a having a pitch longer than that of the inner leads 6a of the first group (sparse pitch region).
Thus, when the inner lead regions have different pitches, the protruding electrodes 11 formed on the inner lead 8a in the sparse pitch region have a height higher than those of the protruding electrodes 9 and 10 formed on the inner leads 6a and 7a in the dense pitch region. When the protruding electrodes have different heights, a failure is likely to occur in a connection between the electrode pad and the protruding electrode when a semiconductor chip is mounted. The reason why a difference occurs between the heights of the protruding electrodes is that the density of a current for plating on the inner lead is higher when the wiring pitch is broad than when the wiring pitch is narrow.